Thermoplastic compositions with enhanced mechanical properties

ABSTRACT

The invention concerns novel reinforced thermoplastic compositions exhibiting an excellent compromise of properties, in particular mechanical properties. More particularly, the invention concerns compositions with slightly filled with small-diameter glass fibers. The compositions have in particular high impact resistance, good rigidity and satisfactory behavior when subjected to relatively high temperatures.

The present invention relates to new reinforced thermoplastic compositions exhibiting an excellent balance of properties, particularly of mechanical properties. The compositions exhibit in particular high impact strength, effective rigidity and satisfactory behavior when subjected to relatively high temperatures.

The properties which it is often desired to enhance for a thermoplastic material intended for forming by techniques such as injection molding, including gas injection molding, extrusion and extrusion blow molding include stiffness, impact strength, dimensional stability, in particular at relatively high temperature, low contraction after forming, capacity for coating by various processes, surface appearance and density. The selection of a material for a given application is generally guided by the performance level which is required in terms of certain properties and by its cost. New materials are always being sought that are capable of meeting a set of specifications in terms of performance and/or cost.

In order to enhance the mechanical properties of a thermoplastic material it is known to introduce glass fibers into the thermoplastic material, as a reinforcing filler. Generally speaking, for a given fiber, the mechanical properties are improved in proportion with the amount of glass fibers in the material. Consequently, reinforced thermoplastic materials intended for forming by molding are often highly filled with glass fibers.

The substantial presence of glass fibers in thermoplastic materials has a number of drawbacks.

A high concentration of glass fibers in a material may give rise to problems during particular treatments of the material, such as the capacity for coating, for example. Moreover, at a high fiber concentration, anisotropy phenomena may appear.

It is likewise known that in the course of introduction, which is generally carried out in an extruder, of glass fibers into a material intended for molding, the glass fibers are broken. Indeed, for a fiber of given original length and given diameter, a decrease in the length of the fiber is observed in the material when the proportion of fibers in the composition increases. The phenomenon of breakage may also be measured by the L/d factor, where L is the length and d is the diameter of the fiber in the material. The higher the proportion of fibers in the material, the lower this factor.

In order to obtain effective enhancement of the mechanical properties it is important to conserve the integrity of the glass fibers introduced into the material, and therefore to limit the phenomenon of breakage in the course of mixing with the material. What is sought in particular is a high L/d factor in order to enhance the properties of reinforcement of the material.

For this purpose the present invention proposes thermoplastic compositions with preferably a low degree of glass fiber filling, which do not exhibit the drawbacks set out above. The invention proposes in particular compositions comprising glass fibers of low diameter. These compositions exhibit an excellent balance between the various mechanical properties desired and the amount of filler introduced.

The present invention likewise relates to thermoplastic compositions which exhibit, in particular, high impact strength while maintaining its other mechanical properties at a good level.

The present invention firstly provides a thermoplastic composition comprising a thermoplastic matrix and glass fibers, characterized in that:

-   -   the glass fibers have a diameter of less than 10 μm,     -   the proportion by weight of the glass fibers relative to the         composition is less than or equal to 50%.

The present invention likewise provides compositions as described above, comprising an impact modifier.

Secondly the present invention provides articles formed from these compositions, especially moldings.

By glass fiber diameter is meant the diameter of the unitary filaments.

The glass fibers in accordance with the invention may be fibers of type E (as defined in “Handbook of Reinforced Plastics”—Ed. 1964, p. 120), whose linear density (weight per kilometer of filament) may vary between 600 and 2500 dtex. Although E fibers are considered to be particularly suitable for the applications for which the compositions in accordance with the invention are intended, it is possible to use other fibers, either exclusively or in combination with E fibers. The aforementioned work indicates (pages 121-122) examples of such fibers.

The glass fibers used to obtain compositions in accordance with the invention preferably have an original length of between 0.3 and 6 mm. It is possible to use continuous filaments.

The glass fibers in accordance with the invention have a diameter of less than 10 μm, preferably less than 9 μm.

These glass fibers in accordance with the invention may be used alone or in combination with other glass fibers with a diameter of greater than 10 μm.

The proportion by weight of the glass fibers relative to the composition is less than or equal to 50%. According to one preferential embodiment of the invention the proportion by weight of the glass fibers in the invention is between 1 and 50% inclusive.

This proportion is advantageously less than or equal to 30%, preferably less than or equal to 20%.

The thermoplastic matrix in accordance with the invention is a thermoplastic polymer. Examples of polymers which may be suitable include the following: polylactones such as poly(pivalolactone), poly(caprolactone) and polymers from the same class; polyurethanes obtained by reaction between diisocyanates such as 1,5-naphthalene diisocyanate; p-phenylene diisocyanate, m-phenylene diisocyanate, 2,4-toluene diisocyanate, 4,4′-diphenylmethane diisocyanate, 3,3′-dimethyl-4,4′-diphenylmethane diisocyanate, 3,3′-dimethyl-4,4′-biphenyl diisocyanate, 4,4′-diphenylisopropylidene diisocyanate, 3,3′-dimethyl-4,4′-diphenyl diisocyanate, 3,3′-dimethyl-4,4′-diphenylmethane diisocyanate, 3,3′-dimethoxy-4,4′-biphenyl diisocyanate, dianisidine diisocyanate, toluidine diisocyanate, hexamethylene diisocyanate, 4,4′-diisocyanatodiphenylmethane and compounds from the same class and linear long-chain diols such as poly(tetramethylene adipate), poly(ethylene adipate), poly(1,4-butylene adipate), poly(ethylene succinate), poly(2,3-butylene succinate), polyether diols and compounds from the same class; polycarbonates such as poly[methanebis(4-phenyl) carbonate], poly[1,1-ether bis(4-phenyl) carbonate], poly(diphenylmethanebis(4-phenyl) carbonate], poly[1,1-cyclohexanebis(4-phenyl) carbonate] and polymers from the same class; polysulfones; polyethers; polyketones; polyamides such as poly(4-aminobutyric acid), poly(hexamethyleneadipamide), poly(6-aminohexanoic acid), poly(m-xylyleneadipamide), poly(p-xylylenesebacamide), poly(2,2,2-trimethyl-hexamethyleneterephthalamide), poly(meta-phenylene-isophthalamide), poly(p-phenyleneterephthalamide), and polymers from the same class; polyesters, such as poly(ethylene azelate), poly(ethylene 1,5-naphthalate), poly(1,4-cyclohexanedimethylene terephthalate), poly(ethylene oxybenzoate), poly(para-hydroxybenzoate), poly(1,4-cyclohexylidenedimethylene terephthalate), poly(1,4-cyclohexylidenedimethylene terephthalate, polyethylene terephthalate, polybutylene terephthalate and polymers from the same class; poly(arylene oxides) such as poly(2,6-dimethyl-1,4-phenylene oxide), poly(2,6-diphenyl-1,4-phenylene oxide) and polymers from the same class; poly(arylene sulfides) such as poly(phenylene sulfide) and polymers from the same class; polyetherimides; vinyl polymers and their copolymers, such as polyvinyl acetate, polyvinyl alcohol, polyvinyl chloride; polyvinyl butyral, polyvinylidene chloride, ethylene-vinyl acetate copolymers, and polymers from the same class; acrylic polymers, polyacrylates and their copolymers, such as polyethyl acrylate, poly(n-butyl acrylate), polymethyl methacrylate, polyethyl methacrylate, poly(n-butyl methacrylate), poly(n-propyl methacrylate), polyacrylamide, polyacrylonitrile, poly(acrylic acid), ethylene-acrylic acid copolymers, ethylene-vinyl alcohol copolymers, copolymers of acrylonitrile, methyl methacrylate-styrene copolymers, ethylene-ethyl acrylate copolymers, methacrylate-butadiene-styrene copolymers, ABS, and polymers from the same class; polyolefins, such as low-density poly(ethylene), poly(propylene), low-density chlorinated poly(ethylene), poly(4-methyl-1-pentene), poly(ethylene), poly(styrene), and polymers from the same class; ionomers; poly(epichlorohydrins); poly(urethane)s such as polymerization products of diols, such as glycerol, trimethylolpropane, 1,2,6-hexanetriol, sorbitol, pentaerythritol, polyether polyols, polyester polyols and compounds from the same class, with polyisocyanates, such as 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 4,4′-diphenyl-methane diisocyanate, 1,6-hexamethylene diisocyanate, 4,4′-dicyclohexylmethane diisocyanate and compounds from the same class; and polysulfones such as the products of reaction of a sodium salt of 2,2-bis(4-hydroxyphenyl)propane and 4,4′-dichloro-diphenyl sulfone; furan resins such as poly(furan); cellulose ester plastics, such as cellulose acetate, cellulose acetate-butyrate, cellulose propionate and polymers from the same class; silicones such as poly(dimethylsiloxane), poly(dimethylsiloxane-co-phenylmethylsiloxane), and polymers from the same class; and mixtures of at least two of the above polymers.

Among these thermoplastic polymers very particular preference is given to semicrystalline polyamides, such as polyamide 6, polyamide 66; polyamide 11, polyamide 12, polyamides 4-6, 6-10, 6-12, 6-36 and 12-12, semiaromatic polyamides, poly-phthalamides obtained from terephthalic and/or isophthalic acid, such as the polyamide sold under the commercial name Amodel, and copolymers and alloys thereof. Other preferred thermoplastic polymers are the alloys of the abovementioned polyamides with other polymers, especially PET, PPO, PBT, ABS or elastomers such as polypropylene.

According to one particular version of the invention the thermoplastic matrix is a polymer comprising H-shaped or star-shaped macromolecular chains and, where appropriate, linear macromolecular chains. Polymers comprising such H-shaped or star-shaped macromolecular chains are, for example, described in documents FR 2 743 077, FR 2 779 730, U.S. Pat. No. 5,959,069, EP 0 632 703, EP 0 682 057 and EP 0 832 149. These compounds are known to exhibit enhanced fluidity relative to linear polyamides. The flow index of the thermoplastic matrix used in the context of this particular version of the invention, measured in accordance with standard ISO 1133 at 275° C. under a load of 325 g, is greater than 20 g/10 min.

The preferred H-shaped or star-shaped macromolecular chains of the invention are chains having a polyamide structure. They are obtained by using a polyfunctional compound having at least three reactive functions, all of the reactive functions being identical. This compound can be used as a comonomer in the presence of other monomers in a polymerization process. It may also be mixed with a polymer melt during an extrusion operation.

The H-shaped or star-shaped macromolecular chains comprise a core and at least three thermoplastic polymer branches, preferably of polyamide. The branches are linked to the core by a covalent bond, via an amide group or a group of another kind. The core is an organic or organometallic chemical compound, preferably a hydrocarbon compound which optionally contains heteroatoms and to which the branches are connected. The branches are preferably polyamide chains. They may exhibit branching sites, which is the case in particular for the H structures. The polyamide chains constituting the branches are preferably of the type obtained by polymerizing lactams or amino acids, of polyamide 6 type, for example.

The thermoplastic matrix according to the particular version of the invention described above optionally comprises, in addition to the H-shaped or star-shaped chains, chains of linear thermoplastic polymer, preferably linear polyamide chains. The ratio by weight between the amount of H-shaped or star-shaped chains in the matrix and the sum of the amounts of H-shaped or star-shaped chains and of linear chains is between 0.1 and 1 inclusive. It is preferably between 0.5 and 1.

According to one preferential embodiment of the particular version of the invention the thermoplastic matrix is a star polyamide, i.e., comprising star-shaped macromolecular chains, which is obtained by copolymerization from a mixture of monomers comprising:

-   -   a) a polyfunctional compound comprising at least three identical         reactive functions selected from the amine function and the         carboxylic acid function,     -   b) monomers of general formulae (IIa) and/or (IIb) as follows:     -   c) optionally monomers of general formula (III) as follows:         Z-R₃-Z   (III)         in which     -   Z represents a function identical to that of the reactive         functions of the polyfunctional compound,     -   R₂ and R₃, which are identical or different, represent         substituted or unsubstituted aliphatic, cycloaliphatic or         aromatic hydrocarbon radicals containing 2 to 20 carbon atoms         and possibly containing heteroatoms,     -   Y is a primary amine function when X represents a carboxylic         acid function, or     -   Y is a carboxylic acid function when X represents a primary         amine function.

By carboxylic acid is meant carboxylic acids and derivatives thereof, such as acid anhydrides, acid chlorides, esters, etc. By amine is meant amines and derivatives thereof.

Processes for obtaining these star-polyamides are described in documents FR 2 743 077 and FR 2 779 730. These processes lead to the formation of star-shaped macromolecular chains, in a mixture with linear macromolecular chains where appropriate.

Where a comonomer c) is used the polymerization (polycondensation) reaction is advantageously carried out until thermodynamic equilibrium is reached.

According to another preferential embodiment of the particular version of the invention the thermoplastic matrix is an H-shaped polyamide obtained by copolymerization from a mixture of monomers comprising:

-   -   a) a polyfunctional compound comprising at least three identical         reactive functions selected from the amine function and the         carboxylic acid function,     -   b) lactams and/or amino acids,     -   c) a difunctional compound selected from dicarboxylic acids or         diamines,     -   d) a monofunctional compound whose function is either an amine         function or a carboxylic acid function,         the functions of c) and d) being amine when the functions of a)         are acid, the functions of c) and d) being acid when the         functions of a) are amine, the ratio in equivalents between the         functional groups of a) and the sum of the functional groups         of c) and d) being between 1.5 and 0.66, and the ratio in         equivalents between the functional groups of c) and the         functional groups of d) being between 0.17 and 1.5.

H-shaped polyamides of this kind and their preparation process are described in patent U.S. Pat. No. 5,959,069.

According to another preferential embodiment of the particular version of the invention the thermoplastic matrix comprising H-shaped or star-shaped macromolecular chains and, where appropriate, linear macromolecular chains is obtained by mixing in the melt, with the aid for example of an extrusion device, of a polyamide, of the type obtained by polymerizing lactams and/or amino acids, and of a polyfunctional compound comprising at least three identical reactive functions selected from the amine function or carboxylic acid function. The polyamide is, for example, polyamide 6.

Preparation processes of this kind are described in patents EP 0 682 070 and EP 0 672 703.

The monomeric polyfunctional compounds from which the H-shaped or star-shaped macromolecular chains of the particular version of the invention originate may be selected from compounds having an arborescent or dendritic structure. They may also be selected from the compounds represented by the formula (IV): R1-[-A-z]_(m)   (IV) in which:

-   -   R₁ is a hydrocarbon radical containing at least two carbon         atoms, which is linear or cyclic, aromatic or aliphatic and may         contain heteroatoms,     -   A is a covalent bond or an aliphatic hydrocarbon radical         containing 1 to 6 carbon atoms,     -   Z represents a primary amine radical or a carboxylic acid         radical, and     -   m is an integer between 3 and 8.

According to one particular feature of the invention the radical R₁ is either a cycloaliphatic radical such as the tetravalent radical of cyclo-hexanonyl or a 1,1,1-propanetriyl or 1,2,3-propanetriyl radical.

Examples of other radicals R₁ suitable for the invention include substituted or unsubstituted trivalent radicals of phenyl and cyclohexanyl, tetravalent radicals of diaminopolymethylene with a number of methylene groups which is advantageously between 2 and 12, such as the radical originating from EDTA (ethylenediaminetetraacetic acid), octavalent radicals of cyclohexanonyl or cyclohexadinonyl, and radicals originating from compounds obtained from the reaction of polyols such as glycol, pentaerythritol, sorbitol or mannitol with acrylonitrile.

The radical A is preferably a methylenic or polymethylenic radical such as ethyl, propyl or butyl radicals, or a polyoxyalkylenic radical such as the polyoxyethylene radical.

According to one particular embodiment of the invention the number m is greater than or equal to 3 and advantageously is 3 or 4.

The reactive function of the polyfunctional compound, represented by the symbol Z, is a function which is capable of forming an amide function.

Preferably the polyfunctional compounds are selected from 2,2,6,6-tetra(β-carboxyethyl)cyclo-hexanone, trimesic acid, 2,4,6-tri(aminocaproic acid)-1,3,5-triazine and 4-aminoethyl-1,8-octanediamine.

The mixture of monomers from which the H-shaped or star-shaped macromolecular chains of the particular version of the invention originate may comprise other compounds, such as chain transfer agents, catalysts and additives, such as light stabilizers and heat stabilizers.

According to another particular version of the invention the thermoplastic matrix of the invention is a polymer of random tree type, preferably a copolyamide having a random tree structure. These copolyamides of random tree structure and their preparation process are described in particular in document WO 99/03909. These copolyamides are of the type obtained by polycondensation of:

-   -   at least one polyfunctional monomer satisfying the following         general formula (V):         (AR₄)—R—(R₅)_(n)   (V)         in which:     -   n is an integer greater than or equal to 2, preferably between 2         and 10 (inclusive),     -   R₄ and R₅ may be identical or different and they represent a         covalent bond or an aliphatic, arylaliphatic, aromatic or         alkylaromatic hydrocarbon radical,     -   R is a linear or branched aliphatic radical, a substituted or         unsubstituted cycloaliphatic radical or a substituted or         unsubstituted aromatic radical possibly comprising two or more         aromatic rings and/or heteroatoms,     -   A represents the amine or amine salt function, or the acid,         ester, acid halide or amide function,     -   B represents the amine or amine salt function when A represents         an acid, ester, acid halide or amide function, and an acid,         ester, acid halide or amide function when A represents an amine         or amine salt function,     -   at least one of the difunctional monomers of, formulae VI to         VIII below with optionally at least one of the monofunctional         monomers of formula IX or X below, or with a prepolymer obtained         from at least one difunctional monomer of formulae VI to VIII         below and optionally at least one monofunctional monomer of         formula IX or X below,     -   the difunctional monomers satisfying the following general         formulae:         A₁—R₇-A₁   (VI)         B₁—R₈—B₁   (VII) and/or         A₁-R₉—B₁ or the corresponding lactams   (VIII)     -   the monofunctional monomers satisfying the following general         formulae:         R₁₀—B₁   (IX), and/or         R₁₁-A₁   (X)         in which:     -   A₁ and B₁ represent respectively an acid, ester, acid halide or         amide function and an amine function or an amine salt,     -   R₇, R₈, R₉, R₁₀ and R₁₁ represent linear or branched alkyl         hydrocarbon radicals, substituted or unsubstituted aromatic         hydrocarbon radicals or alkylaryl, arylalkyl or cycloaliphatic         hydrocarbon radicals which may include unsaturations.

The thermoplastic matrix of the invention may also be a composition comprising a linear thermoplastic polymer and a thermoplastic star, H-shaped and/or tree polymer as described above.

The compositions of the invention may also comprise a hyperbranched copolyamide of the type described in document WO 00/68298.

The compositions of the invention may also comprise any combination of above-described hyperbranched copolyamide, tree, H-shaped or star thermoplastic polymer.

According to one preferential embodiment of the invention the compositions comprise, further to a thermoplastic matrix and glass fibers, an impact modifier.

Preferred modifiers of the invention are polyolefins with or without an elastomeric nature. It is also possible to use elastomers.

According to one preferred feature of the invention at least some of the compounds modifying the resilience of the composition contain polar functions capable of reacting with the polyamide. These polar functions may be, for example, acid, ester, anhydride, glycidyl or carboxylate functions such as maleic anhydride, acrylic, methacrylic or epoxy functions.

These functions are generally grafted or copolymerized onto the macromolecular chain of the compounds.

Suitable polyolefins for the invention include polyethylenes, polypropylenes, polybutylenes or copolymers of ethylene and α-olefins such as ethylene/propylene dienes, copolymers of ethylene and propylene, EPDMs, EPR, polystyrene butadiene ethylene, such as styrene ethylene butadiene styrene (SEBS), copolymers of polyolefins with vinyl acetate, with acrylate and/or with acrylic acid, and ionomers. These polyolefins may be used as a mixture or as copolymers.

With preference it is possible to use an ethylene-methyl acrylate-glycidyl methacrylate (E-MA-GMA) terpolymer elastomer and/or an ethylene-glycidyl methacrylate (E-GMA) copolymer elastomer.

Impact modifiers suitable for the invention also include nitrile rubbers and silicone elastomers.

Generally speaking it is possible in accordance with the invention to use any polymer having the capacity to modify the impact strength.

The compositions of the invention comprising an impact modifier exhibit in particular excellent impact resistance, even at low modifier concentrations, which represents an economic advantage in particular.

The proportion by weight of the modifier in the compositions of the invention is advantageously less than 10%, preferably less than 8%.

It is specified that the compositions of the invention may include other compounds. These compounds may be stabilizing, pigmenting, flame retarding or catalyzing compounds or other reinforcing compounds. They may also include mineral fillers, such as kaolin, wollastonite, talc, nanoparticles or reinforcing fibers other than the glass fibers of the inventions such as other fibers of glass or of carbon or mineral fibers. These other compounds or fillers or fibers may be introduced into the composition during steps of its manufacture. It is also possible to use polymeric fibers such as kevlar for example.

Details will now be given of processes which can be used for preparing a composition according to the invention.

The thermoplastic compositions are generally obtained by mixing the various compounds forming part of the composition, the thermoplastic compounds being in melt form. A more or less high temperature and a more or less high shear force is used, depending on the nature of the various compounds. The compounds may be introduced simultaneously or in succession. All of the means known to the skilled worker concerning the introduction of the various compounds of a composition in the melt state may be used. An extrusion device is generally used in which the material is heated, subjected to a shear force, and conveyed. Such devices are very well known to the skilled worker.

According to one embodiment all of the compounds are mixed in the melt phase in a single operation, for example an extrusion operation. It is possible, for example, to mix granules of the polymeric materials, to introduce them into the extrusion device in order to melt them and to subject them to greater or lesser shearing, and to introduce the glass fibers and, where appropriate, the other compounds. According to one version it is possible to introduce the glass fibers in the form of a concentrated mixture of the matrix and glass fibers, prepared for example by mixing in the melt phase. It is likewise possible to introduce the impact modifier in the form of a concentrated mixture of the matrix and the modifier. The compositions of the invention may also be prepared by a pultrusion process known to the skilled worker.

When it is prepared using an extrusion device, the composition according to the invention is preferably processed in granule form.

The composition, or more specifically the granules, is intended for forming with the aid of processes which involve melting in order to obtain articles. The articles are therefore composed of the composition. The articles in question may be moldings for example.

The use of the compositions according to the invention is particularly advantageous in the context of the manufacture of articles for the automotive industry, in particular for the manufacture of bodywork components.

Other details or advantages of the invention will emerge more clearly on reading the examples which are given below solely by way of indications

Compounds Used

Compound A1: polyamide 66 of relative viscosity 2.6, measured in sulfuric acid at 95.7% in accordance with standard ISO 307

Compound A2: star polyamide obtained by copolymerization from caprolactam in the presence of 0.48% molar of 2,2,6,6-tetra(β-carboxyethyl)cyclo-hexanone, by a process described in document

FR 2743077, containing approximately 80% of star-shaped macromolecular chains and 20% of linear macromolecular chains, with a melt flow index, measured at 275° C. under 325 g, of 45 g/10 minutes.

Compound A3: star polyamide obtained by copolymerization from caprolactam in the presence of 0.41% molar of 2,2,6,6-tetra(β-carboxyethyl)cyclo-hexanone, by a process described in document

FR 2743077, containing approximately 80% of star-shaped macromolecular chains and 20% of linear macromolecular chains, with a melt flow index, measured at 275° C. under 325 g, of 30 g/10 minutes.

Compound B1: glass fibers 6.5 μm in diameter and 3±1 mm in length, sold by NEC Nippon Electric Glass under the reference ECS-03T289DE.

Compound B2: glass fibers 7 μm in diameter and 4.5 mm in length

Compound B3: glass fibers 10 μm in diameter and 4.5 mm in length

Compound C: impact modifier sold by Exxon Mobil under the reference Exxelor 1803, elastomeric copolymer of ethylene functionalized with maleic anhydride.

Compound D: ethylene-methyl acrylate-glycidyl methacrylate E-MA-GMA terpolymer elastomer sold by Atofina under the reference Lotader® Grade AX 8920.

Preparation of the Compositions

The compositions were prepared by mixing in the melt phase using a WERNER & PFLEIDERER ZSK 25 twin-screw extruder. The extrusion conditions were as follows:

-   -   Temperature: between 260 and 280° C. (examples 1, 2, 5 to 10),         between 230 and 250° C. (examples 3 and 4),     -   Rotational speed: 250 rpm     -   Throughput 18 kg/hour.         Forming of the Compositions

The compositions after extrusion are injection molded using an Arbug 320M machine. The injection conditions are of the following type:

-   -   Temperature: 270° C. (examples 1, 2, 5 to 10), between 220 and         235° C. (examples 3 and 4)     -   Injection rate: 70 cm³/s (examples 1, 2, 5 to 10) ; 80 cm³/s         (examples 3 and 4)     -   Injection pressure: 1300 bars     -   Mold temperature: 80° C.         Evaluations

The mechanical properties of the compositions are evaluated as follows:

-   -   tensile modulus in accordance with standard ISO 527, measured         after conditioning of the test specimen at 23° C. in the dry         as-molded state at a relative humidity of 50% in accordance with         standard ISO 1874-2     -   breaking stress in accordance with standard ISO 527, measured         after conditioning of the test specimen at 23° C. in the dry         as-molded state at a relative humidity of 50% in accordance with         standard ISO 1874-2     -   breaking elongation in accordance with standard ISO 527,         measured after conditioning of the test specimen at 23° C. in         the dry as-molded state at a relative humidity of 50% in         accordance with standard ISO 1874-2     -   notched IZOD impact strength in accordance with standard ISO         180\1A, measured after conditioning of the test specimen at         23° C. in the dry as-molded state at a relative humidity of 50%         in accordance with standard ISO 1874-2     -   unnotched IZOD impact strength in accordance with standard ISO         180\1U, measured after conditioning of the test specimen at         23° C. in the dry as-molded state at a relative humidity of 50%         in accordance with standard ISO 1874-2     -   temperature of deformation under load (HDT—heat deflection         temperature) in accordance with standard ISO 75Ae, under a load         of 1.8 N/mm²

EXAMPLES 1-2 PA66+6.5 μm diameter glass fiber compositions

The compositions prepared are shown in table I. The percentages in table I are percentages by mass. TABLE I Example A B 1 2 (comparative) (comparative) Compound A1 (%) 90 85 90 85 Compound B1 (%) 10 15 — — Compound B3 (%) — — 10 15

The properties are shown in table II TABLE II Example 1 A 2 B Tensile modulus (N/mm²) 4830 4830 5760 5810 Breaking stress (N/mm²) 121 109 145 130 Breaking elongation (%) 3.6 2.8 4.1 2.8 Unnotched IZOD impact strength 44 32 49 34 (kJ/m²) Notched IZOD impact strength 4.4 5.7 5.2 7.4 (kJ/m²)

For a given proportion by weight of glass fibers, the compositions of the invention comprising glass fibers of diameter 6.5 μm exhibit in particular a breaking stress and an unnotched IZOD impact strength (and a breaking elongation) which are enhanced relative to the compositions comprising glass fibers of diameter 10 μm.

EXAMPLES 3-4 Star Polyamide+Glass Fiber Compositions

The compositions prepared are shown in table III. The percentages in table III are percentages by mass. TABLE III Example C D 3 4 (comparative) (comparative) Compound A2 (%) 90 85 90 85 Compound B2 (%) 10 15 — — Compound B3 (%) — — 10 15

The properties are shown in table IV TABLE IV Example 3 C 4 D Tensile modulus (N/mm²) 5170 5150 6420 6210 Breaking stress (N/mm²) 106 77 130 94 Breaking elongation (%) 2.5 1.6 2.6 1.7 Unnotched IZOD impact strength 26 15 30 20 (kJ/m²)

For a given proportion by weight of glass fibers, the compositions of the invention comprising glass fibers of diameter 7 μm exhibit in particular a breaking stress and an unnotched IZOD impact strength (and a breaking elongation) which are enhanced relative to the compositions comprising glass fibers of diameter 10 μm.

FIG. 1 represents a graph describing the change in the factor L/d (ratio of the length of the glass fibers to the diameter of the fibers) as a function of the proportion by weight of the glass fibers in the composition.

This change is measured following extrusion and injection molding of compositions comprising as their thermoplastic matrix the compound A2, by dissolving the compositions in formic acid, with measurements under the microscope.

This change is measured on these compositions for different fiber diameters (10, 6.5 and 7 μm), each fiber diameter corresponding to a curve on the graph. The compositions comprising fibers with diameters of 6.5 and 7 μm, at proportions by weight of glass fibers of less than or equal to 50%, exhibit a higher L/d factor than the compositions comprising fibers of diameter 10 μm. The L/D factor of the fibers is retained better for fibers of low diameter (6.5 and 7 μm) than for fibers of greater diameter (10 μm).

Examples 5-7 PA66+6.5 μm Diameter Glass Fiber+Impact Modifier Compositions

The compositions prepared are shown in table V. The percentages in table V are percentages by mass. TABLE V Example E F G (compar- (compar- (compar- 5 6 7 ative) ative) ative) Compound A1 (%) 90 85 80 90 85 80 Compound B1 (%) 5 10 15 — — — Compound B3 (%) — — — 5 10 15 Compound C (%) 5 5 5 5 5 5

The properties are shown in table VI TABLE VI Example 5 E 6 F 7 G Tensile modulus (N/mm²) 3770 3800 4550 4720 5540 5600 Breaking stress (N/mm²) 84 86 111 103 132 118 Breaking elongation (%) 9.8 6.1 4.9 4.8 4.1 4.2 Notched IZOD impact strength 7.3 3.7 9.6 5.3 12.3 8.0 (kJ/m²) Unnotched IZOD impact 58 34 61 45 68 59 strength (kJ/m²) Temperature of deformation 207 186 229 234 244 239 under load (° C.)

For a given proportion of glass fibers, the compositions of the invention comprising fibers of diameter 6.5 μm exhibit in particular a notched and unnotched IZOD impact strength which is enhanced relative to compositions comprising fibers of diameter 10 μm.

Examples 8-10 PA66+7 μm Diameter Glass Fiber+Impact Modifier Compositions

The compositions prepared are shown in table VII. The percentages in table VII are percentages by mass. TABLE VII Example 8 9 10 Compound A1 (%) 90 85 80 Compound B2 (%)  5 10 15 Compound B3 (%) — — — Compound C (%)  5  5  5

The properties are shown in table VIII TABLE VIII Example 8 E 9 F 10 G Tensile modulus (N/mm²) 3770 3800 4580 4720 6200 5600 Breaking stress (N/mm²) 87 86 112 103 142 118 Breaking elongation (%) 8.4 6.1 5.1 4.8 4.3 4.2 Notched IZOD impact strength 5.1 3.7 6.9 5.3 11.4 8.0 (kJ/m²) Unnotched IZOD impact 45 34 64 45 65 59 strength (kJ/m²) Temperature of deformation 220 186 228 234 243 239 under load (° C.)

For a given proportion of glass fibers, the compositions of the invention comprising fibers of diameter 7 μm exhibit in particular a notched and unnotched IZOD impact strength which is enhanced relative to compositions comprising fibers of diameter 10 μm.

EXAMPLE 11 Influence of the Diameter of the Fiber on the Enhancement of the Notched IZOD Impact Strength When Modifier is Introduced Into PA66 Compositions

The increase in the notched IZOD impact strength when 5% of modifier is introduced into the compositions of example 1 (corresponding after introduction to example 6), 2 (corresponding after introduction to example 7), A (corresponding after introduction to example F) and B (corresponding after introduction to example G) TABLE IX Example 1 2 A B Percentage increase in notched +118.2 +136.5 −7 +8.1 IZOD impact strength (%)

For a given proportion of glass fibers, the introduction of 5% of impact modifier into the compositions of the invention comprising glass fibers of diameter of 6.5 μm leads to a markedly greater enhancement of the notched IZOD impact strength than the introduction of 5% of impact modifier into compositions comprising glass fibers of diameter 10 μm.

EXAMPLES 12-17 Star Polyamide+Glass Fiber+Impact Modifier Compositions

The compositions prepared are shown in table X. The percentages in the table are percentages by mass. Their properties are shown in table XI. TABLE X Example 12 13 14 15 16 17 H I J Compound A3 (%) 95 90 85 94 89 84 94 89 84 Compound B1 (%) 5 10 15 5 10 15 — — — Compound B3 (%) — — — — — — 5 10 15 Compound D (%) — — — 1 1 1 1 1 1

TABLE XI Example 12 13 14 15 16 17 H I J Tensile modulus (N/mm²) 4930 5670 6650 3660 4690 5450 3780 5100 6230 Breaking stress (N/mm²) 85 100 120 90 115 139 84 92 110 Breaking elongation (%) 2.1 2.0 2.3 3.1 3.2 3.5 2.8 2.8 3.1 Notched IZOD impact strength (kJ/m²) 4.5 6.5 6.9 5.0 7.5 8.0 4.5 5.8 6.7 Unnotched IZOD impact strength (kJ/m²) 29 32 36 35 37 42 21 23 24 Temperature of deformation under load (° C.) — 193 202 — 194 198 — 187 195

For a given proportion of glass fibers, the compositions of the invention comprising a star polyamide and fibers of diameter 6.5 μm exhibit in particular a notched and unnotched IZOD impact strength which is enhanced relative to compositions comprising fibers of diameter 10 μm. The mechanical properties are also increased in the presence of an impact modifier compound. 

1-22. (Canceled)
 23. A thermoplastic composition comprising: a thermoplastic matrix, glass fibers having a diameter of less than 10 μm, with a proportion by weight of the glass fibers relative to the composition being less than or equal to 50%, and an impact modifier.
 24. The composition as claimed in claim 23, wherein the proportion by weight of the glass fibers relative to the composition is between 1 and 50%.
 25. The composition as claimed in one of the preceding claims, wherein the proportion by weight of the glass fibers relative to the composition is less than or equal to 30%.
 26. The composition as claimed in claim 25, wherein the proportion by weight of the glass fibers relative to the composition is less than or equal to 20%.
 27. The composition as claimed in claim 23, wherein the glass fibers present a diameter of less than or equal to 9 μm.
 28. The composition as claimed in claim 23, wherein the impact modifier is an elastomer.
 29. The composition as claimed in claim 23, wherein the impact modifier is present in a proportion by weight relative to the composition of less than 10%.
 30. The composition as claimed in claim 29, wherein the proportion of the impact modifier by weight relative to the composition is less than 8%.
 31. The composition as claimed in claim 23, wherein the thermoplastic matrix is polyamide 6, polyamide 66, polyamide 11, polyamide 12, polyamides 4-6, 6-10, 6-12, 6-36 and 12-12, a semiaromatic polyamide, a copolymer thereof, an alloy thereof, or an alloy of these polyamides with PET, PPO, PBT or ABS.
 32. The composition as claimed in claim 23, wherein the thermoplastic matrix is a thermoplastic polymer comprising H-shaped or star-shaped macromolecular chains having one or more cores and at least three branches or three polyamide segments connected to a core, linear macromolecular chains, said thermoplastic matrix having a melt flow index, measured in accordance with standard ISO 1133 at 275° C. under a load of 325 g, greater than 20 g/10 min.
 33. The composition as claimed in claim 32, wherein the H-shaped or star-shaped macromolecular chains and the sum of the H-shaped or star-shaped macromolecular chains and the linear chains in the thermoplastic matrix, present a ratio by weight of between 0.1 and
 1. 34. The composition as claimed in claim 32, wherein the thermoplastic matrix is a star polyamide obtained by copolymerization from a mixture of monomers comprising: a) a polyfunctional compound having at least three identical reactive functions being an amine function or a carboxylic acid function, b) monomers of general formulae (IIa) or (IIb) as follows:

c) optionally, monomers of general formula (III) as follows: Z-R₃-Z   (III) wherein: Z represents a function identical to that of the reactive factions of the polyfunctional compound, R₂ and R₃, which are identical or different, represent substituted or unsubstituted aliphatic, cycloaliphatic or aromatic hydrocarbon radicals containing 2 to 20 carbon atoms and, optionally, heteroatoms, Y is a primary amine function when X represents a carboxylic acid function, or Y is a carboxylic acid function when X represents a primary amine function.
 35. The composition as claimed in claim 32, wherein the thermoplastic matrix is an H-shaped polyamide obtained by copolymerization from a mixture of monomers comprising: a) a polyfunctional compound comprising at least three identical reactive functions being an amine function or a carboxylic acid function, b) lactams or amino acids, c) a difunctional compound being a dicarboxylic acid or a diamine, d) a monofunctional compound whose function is either an amine function or a carboxylic acid function, the functions of c) and d) being amine when the functions of a) are acid, the functions of c) and d) being acid when the functions of a) are amine, said functions having a ratio in equivalents between the functional groups of a) and the sum of the functional groups of c) and d) of between 1.5 and 0.66, and a ratio in equivalents between the functional groups of c) and the functional groups of d) of between 0.17 and 1.5.
 36. The composition as claimed in claim 32, wherein the thermoplastic matrix is obtained by extrusion of a mixture of polyamide obtained by polymerizing lactams or amino acids and a polyfunctional compound comprising at least three identical reactive functions being an amine function or a carboxylic acid function.
 37. The composition as claimed in claim 34, wherein the polyfunctional compound exhibits an arborescent or dendritic structure.
 38. The composition as claimed in claim 34, wherein the polyfunctional compound is represented by the formula (I) R1-[-A-z ]_(m)   (I) wherein: R₁ is a hydrocarbon radical having at least two carbon atoms, which is linear or cyclic, aromatic or aliphatic and optionally containing heteroatoms, A is a covalent bond or an aliphatic hydrocarbon radical having 1 to 6 carbon atoms, Z represents a primary amine radical or a carboxyl group, and m is an integer between 3 and
 8. 39. The composition as claimed in claim 38, wherein the polyfunctional compound is 2,2,6,6-tetra(β-carboxyethyl)cyclohexanone, trimesic acid, 2,4,6-tri(aminocaproic acid)-1,3,5-triazine or 4-aminoethyl-1,8-octanediamine.
 40. The composition as claimed in claim 23, wherein the thermoplastic matrix is a copolyamide of random tree structure, obtained by polycondensation of: at least one polyfunctional monomer satisfying the following general formula (V): (AR₄)—R—(R₅)_(n)   (V) wherein: n is an integer greater than or equal to 2, between 2 and 10 (inclusive), R₄ and R₅, identical or different, represent a covalent bond, an aliphatic, arylaliphatic, aromatic or alkylaromatic hydrocarbon radical, R is a linear or branched aliphatic radical, a substituted or unsubstituted cycloaliphatic radical or a substituted or unsubstituted aromatic radical, optionally comprising two or more aromatic rings or heteroatoms, A represents an amine function, an amine salt function, an acid function, ester function, acid halide function, or amide function, B represents an amine or amine salt function when A represents an acid, ester, acid halide or amide function, and an acid, ester, acid halide or amide function when A represents an amine or amine salt function, at least one of the difunctional monomers of formulae VI to VIII below with optionally at least one of the monofunctional monomers of formula IX or X below, or with a prepolymer obtained from at least one difunctional monomer of formulae VI to VIII below and optionally at least one monofunctional monomer of formula IX or X below, the difunctional monomers satisfying the following general formulae: A₁-R₇-A₁   (VI) B₁—R₈—B₁   (VII) or A₁-R₉—B₁ or the corresponding lactams   (VII) the monofunctional monomers satisfying the following general formulae: R₁₀—B₁   (IX), or R₁₁-A₁   (X) wherein: A₁ and B₁ represent respectively an acid, ester, acid halide or amide function and an amine function or an amine salt, R₇, R₈, R₉, R₁₀ and R₁₁ represent linear or branched alkyl hydrocarbon radicals, substituted or unsubstituted aromatic hydrocarbon radicals or alkylaryl, arylalkyl or cycloaliphatic hydrocarbon radicals, optionally including unsaturations.
 41. The composition as claimed in claim 23, wherein the thermoplastic matrix is a composition comprising a linear thermoplastic polymer and a thermoplastic star, H-shaped or tree polymer.
 42. The composition as claimed in claim 23, comprising a hyperbranched copolyamide.
 43. The composition as claimed in claim 23, further comprising an additive selected from the group consisting of stabilizing, pigmenting, flame retarding, catalyzing compound, reinforcing compound or a mineral filler.
 44. An article formed from a composition as claimed in claim
 23. 